Servicio Geológico Colombiano’s (SGC) Observatorio Vulcanológico y Sismológico de Manizales reported that the eruption at Nevado del Ruiz continued at low-to-moderate levels during 17-23 October. Seismic events indicating the movement of fluids increased in number and intensity compared to the previous week. The number of signals indicating rock fracturing increased in intensity, though decreased in number. These events were located in areas as far as 13 km ESE and SW of Arenas Crater, at depths less than one to 7 km. Earthquakes recorded at 2214 on 21 October (M 3) and at 0837 on 22 October (M 3.2) were felt by residents in the municipality of Murillo. Thermal anomalies on the crater floor were identified in satellite images, though they were less intense than the previous week. Several ash-and-gas emissions were visible during the week, with the highest plumes rising to 1.6 km above the crater rim on 17 October. Plumes drifted SW, NW, and NNE. The Alert Level remained at Yellow, Level III (the second level on a four-level scale).

Geological Summary. Nevado del Ruiz is a broad, glacier-covered volcano in central Colombia that covers more than 200 km2. Three major edifices, composed of andesitic and dacitic lavas and andesitic pyroclastics, have been constructed since the beginning of the Pleistocene. The modern cone consists of a broad cluster of lava domes built within the caldera of an older edifice. The 1-km-wide, 240-m-deep Arenas crater occupies the summit. The prominent La Olleta pyroclastic cone located on the SW flank may also have been active in historical time. Steep headwalls of massive landslides cut the flanks. Melting of its summit icecap during historical eruptions, which date back to the 16th century, has resulted in devastating lahars, including one in 1985 that was South America's deadliest eruption.

Source: Servicio Geológico Colombiano (SGC)